Wire grids are polarization components commonly used in the field of optics or electromagnetic waves, and disclosed in, for example, Non-Patent Document 1. Furthermore, Patent Document 1 discloses the use of a wire grid for a terahertz band ellipsometer.
FIG. 1 is a diagram illustrating the structure of a wire grid. The terahertz band wire grid has, as shown in FIG. 1, thin and long single metal wires 1 arranged at regular intervals with respect to a frame body 2. The metal wires 1 are, for example, tungsten wires of 5 μm to 50 μm in diameter, which are one by one attached to a metallic frame body with an adhesive at a pitch on the order of 10 to 100 μm.
The diameter of the metal wire and the pitch for the metal wire are determined depending on the wavelength used. In the terahertz band, the metal wire has a diameter on the order of 10 to 300 μm, and a pitch on the order of 30 μm to 1 mm.    Patent Document 1: Japanese Patent Application Laid-Open No. 2003-14620    Non-Patent Document 1: Kunio Yoshihara, “Physical Optics”, (KYORITSU SHUPPAN CO., LTD., the first edition in 1966) p. 216
When such a wire grid is used as a terahertz band polarizer, the size of the wire grid ranges from 20 mm to approximately 100 mm in diameter. In the case of a wire grid with a diameter of 100 mm, metal wires have a length of about 100 mm, and it is thus difficult to tighten the long thin metal wires parallel to each other. More specifically, the tension easily cuts the metal wires, or causes an interval between the metal wires to get irregular, thus leading to difficulty in manufacture. Therefore, the wire grid will be very expensive as a component.
On the other hand, there are sold wire grids which are made by forming a thin film on a substrate through which electromagnetic waves are to be transmitted and making the thin film into fine wire patterns by etching or the like. Furthermore, there are also sold wire grids which are made by dispersing metal grain in a base material such as resin or glass, and making the base material into fine wires in the base material by stretching or the like. In the structures with these substrate or base material, phenomena such as multiple reflection or interference occur due to physical properties such as the index of refraction, reflectivity, and absorption index of the substrate or base material. Therefore, special treatment will be required in order to avoid the phenomena.
Furthermore, both the wire grid with the use of the metal wires and the wire grid with the use of the substrate or base material are limited in size up to a diameter on the order of 100 to 150 mm, and it is difficult to make larger wire grids over the size limit.